The present invention relates to a thermal transfer plate (TTP) for coupling a thermal hardware element to an integrated circuit package. In particular, the thermal transfer plate includes protrusions that control the spacing between the integrated circuit and the TTP.
Semiconductor chips produce heat when powered up and operated. Consequently, a thermally conductive plate having a surface area larger than the semiconductor chip is typically used to transfer heat to a heat sink or another type of thermal management hardware. FIG. 1 is a side view of a prior art electrical assembly 10 including a semiconductor chip 2 that generates heat, a printed circuit board (PCB)4, a thermally conductive plate 5, a heat sink 6, and a clamping structure 7. The semiconductor chip 2 is thermally coupled to the thermal plate 5 by a thin layer of conductive material 8 or thermal grease, which minimizes the thermal impedance between the two components. The chip 2 is connected to the substrate 4 by means of an array of solder ball connections 9. The thermal plate 5 contains mounting points for the heat sink 6. Screws 11 connect the plate 5 to the circuit board 4 through fixed standoffs 12.
The gap between the conductive plate 5 and the top surface of the semiconductor chip 2 must not be too close because the two surfaces should be covered entirely by the thermal grease. Non-wetted areas increase the effective thermal resistance between the plate and the semiconductor chip in those areas. Care must also be taken to ensure that the gap between the top surface of the integrated circuit and the thermal plate is not too wide because wider gaps, even when they are filled with thermal grease, degrade thermal performance.
The electrical assembly 10 is typically incorporated into a computer which may be subjected to external shock and vibration loads. Such external vibrations may create a physical separation between the thermal plate 5 and the semiconductor chip 2. Any separation will increase the thermal impedance between the thermal plate and the semiconductor chip and cause an increase in the junction temperatures of the integrated circuit. In addition, any relative movement between the thermal plate and the semiconductor chip may xe2x80x9cpumpxe2x80x9d the thermal grease out of the thermal interface. A reduction in thermal grease will also increase the thermal impedance, resulting in an increase in the junction temperatures of the integrated circuit.
Since the thermal plate 5 mounts on fixed standoffs 12, the stand-off height 14 must be great enough to assure that the top surface of the integrated circuit component 2 on the substrate 4 does not bottom out against a bottom surface of the thermal plate 5. Thus, when an electrical assembly 10 is being designed, a designer must compensate for varying tolerances. In particular, using the printed circuit board 4 as the references, a designer must consider the tolerances in the flatness of the PCB, the semiconductor thickness tolerance, the collapsed solder-ball-height tolerance, the thermally conductive plate flatness, the thermal plate standoff-height tolerance and several other tolerance measures.
New generation integrated circuits, such as faster CPU semiconductor chips, generate more heat. It would thus be desirable to modify the assembly shown in FIG. 1 to optimize and control the gap between the semiconductor chip and the thermally conductive plate, and to prevent separation between the thermal element and the integrated circuit package to ensure adequate cooling of the integrated circuit. It would also be desirable to mitigate or eliminate substantially all of the tolerance accumulations described above.
Presented is a thermal transfer plate for coupling thermal hardware to a substrate that includes an integrated circuit. The thermal transfer plate includes a thermally conductive plate and at least one footpad. The footpad is connected to the plate by way of a spring zone and a standoff member. The TTP includes at least one reference protrusion. In one implementation, the reference protrusion contacts a top surface of a substrate. In another implementation, the TTP includes a die cavity having at least one reference protrusion for contacting a top surface of an integrated circuit die.
A thermal transfer plate according to the invention substantially eliminates tolerance accumulations which plague the design of electrical assemblies. Further, if the reference protrusions are formed by using a precision forming-die, then the gap between the top portion of the integrated circuit and the plate can be reduced. Such thin gaps transfer more heat which permits use of the thermal transfer plate with faster running, and thus hotter, semiconductor devices. Yet further, a TTP according to the invention prevents an inverted impact shock from separating the TTP from the integrated circuit die.
Other advantages and features of the invention will be apparent from the following description and from the claims.